If you are developing web application on Google App Engine for Java. And you dont know what this exception is. You can be in trouble. The container throws this exception for those requests which take time more than 30 seconds. In other words GAE wants every requests to be fullfilled within 30 seconds.

Case

I am developing a Twitter application and I got this exception when I login my Twitter user name. I have some 120 friends and 170 followers. So I need to fill two lists of Twitter users with their name and image URL. It was a bad practice from my side that I started populating lists in a loop which contain external service lookup overhead (Twitter) and also big in iteration. So I got following exception.
This request (670f658c2bf64b44) started at 2009/10/02 23:18:23.902 UTC and was still executing at 2009/10/02 23:18:52.605 UTC.

Possible solution

As for those users who have friends and followers in thousands, this problem will persist. So what I am thinking is to put lists in session. Populate the page with first 30 users. And give a link to next 30 (paginate). I will keep updating two variables in session which will tell start and end to pick the users from the list. I will use DWR for this. By this my every request will be responded by container with in 30 seconds.

If you guys have some more optimum solution for it, please share me. Another solution has been discussed here too.